30 APPLICATION OF THE LAWS OF HYDRAULICS
of the method of computation which is used for an updraft
From a reheating furnace at the Lougansk works (Russia) the
products of combustion, at a temperature of 600°, pass to a boiler
by an outlet port in the roof. The volume of these gases, based
upon the actual coal consumption per second, is computed as being
equal to $500 = 8 m3 58 per second, with an air supply equal to
one and one-half times the theoretical amount required. The
port in the roof of the furnace had a section of 2.5X0.6= 1 m2 50.
With these conditions fixed, at what distance below the roof will
the free surface of the layer of gases in the furnace be located?
8.58 = KHC2
Assuming /ci/c2 = l, V2g = 4A3, it will be found that
And therefore, according to these calculations, the distance
from the free lower surface of the gas layer to the port, in the
case of the gases flowing into the air, would be 896 mm. In the
furnace this distance actually was 800 mm.
This shows that the designers of this furnace had taken into
account a very old rule which says that if a reverbatory furnace is
to work well, the flame must KcA the hearth of the furnace. The
height of 896 mm not only assures the contact of the flame with
the sole of the furnace, but also permits, by the increase or diminu-
tion of the draft through the boiler, of the regulation of the
thickness of the gaseous current; that is to say, it provides a
means of drawing the flame up from the hearth or of forcing it
down against it.
Although the above computation has already been given, it is
repeated here that the port for the waste gases should never be
placed in the roof of the furnace. It is a bad system and one that
is now out of date. In the operation of those furnaces where